In modern processes for brass-plating of long-size articles use is made either of electrolytical brass-plating processes contemplating the use of complex-salt, mainly cyanides, aqueous electrolytes for plating of articles preliminarily heat-treated, or processes of separate electrolytical copper-plating and zinc-plating from aqueous solutions, followed by thermodiffusion treatment and tempering.
However, these brass-plating processes are rather multioperational ones and appropriate apparatus are low-productive and do not enable intensification of the process mainly due to an insufficient heat exchange in muffle furnaces. Carrying out the process of heat-treatment within a wide temperature range is hindered due to temperature drop across the furnace muffles thus producing a detrimental effect to the uniformity of the properties of the resulting articles. Furthermore, stacks of furnaces often have local burning-through, the gas composition is changed or the gas is absent altogether, thus producing a negative effect on one of the main properties of brass-plated articles--tenacity of adherence to rubber.
Known in the art is a process for making brass-plated long-size articles (cf. USSR Inventor's Certificate No. 150727 Int. Cl. C 23 D 5/52 published in "Bulletin of Discoveries, Inventions, Industrial Designs and Trademarks", No. 19, 1962, p. 52) by way of degreasing and etching of the blank surface, coating its surface with a layer of copper, electrolytical zinc-plating of the blank surface, thermodiffusive treatment and tempering of the blank, followed by finishing of the articles. In this process degreasing and etching of a blank are effected successively in solutions of alkalis and acids with application of electric current.
Deposition of copper and zinc layers onto the surface of a blank is effected electrolytically from aqueous solutions, while thermodiffusive treatment and tempering of the blank are effected by heating with a convective heat exchange in the air medium.
However, the prior art process due to the use of solutions of alkalis and acids necessitates an increased rate of water consumption for washing of articles and neutralization of the spent liquors. In doing so, the spent solutions especially those containing complex compounds of copper hardly susceptible to regeneration bring about pollution of water basins.
Owing to oxidation of the surface of a brass-plated long-size article during the heat-treatment according to the prior art process, for a better adherence e.g. to rubber, additional etching of its surface in acid solutions is required, which results in an inefficient consumption of non-ferrous metal.
Furthermore, in the manufacture of a brass-plated long-size article by the process referred to hereinabove, a plastic deformation is inevitably observed due to bending of the article, which necessitates subsequent straightening of the latter, thus resulting in impaired quality characteristics thereof and, in the first place, in respect of adherence to rubber.
Known in the art is an apparatus for making brass-plated long-size articles by the above-disclosed process and comprising disposed along the direction of movement of a blank: a unit for degreasing and etching of the blank surface, a bath with a solution for copper-plating of the blank surface, a unit for electrolytical plating of the blank with a zinc layer, incorporating a bath with a solution for electrolysis, wherein there are provided an anode, a unit for heating the blank, a unit of a thermodiffusive treatment and tempering of the blank, as well as a unit for straightening of the blank.
In this apparatus as the unit for degreasing and etching, as well as a unit for electrolytical coating of the blank surface with a layer of zinc, use is made of electrolytical baths with appropriate solutions for electrolysis; as a unit for thermodiffusive treatment and tempering use is made of a tubular furnace with a convective heat transfer; as the unit for straightening of the blank use is made of a roller straightening means.
However, in this apparatus the baths with a solution for etching, degreasing, copper- and zinc-plating have a considerable length and equipped with sophisticated and expensive electroplating equipment. The process and apparatus described hereinabove also feature considerable inefficient consumption of copper and zinc.
The tubular furnace employed in the above-described apparatus for thermodiffusive treatment and tempering of a blank does not make it possible to intensify the process, since elevation of temperature above 520.degree. C. results in a considerable evaporation of zinc, while extension of its length causes substantial heat losses and rapid deterioration of furnace stacks.
In addition, the above-disclosed apparatus is difficult in servicing and maintenance due to a considerable length of its assemblies and units and difficulties associated with introducing of a long-size article thereinto.